Conventional jointing and finishing of plasterboard sheets utilises a relatively complicated and time consuming process. Conventional jointing and finishing of plasterboard interior installations is typically carried out in accordance with table 1 shown below, and the following details, so as to provide a smooth wall surface for decorating.                Stopping and external corner beads are to be applied to all edges subject to damage.        A “Level 4” Finish is generally the accepted level of finish for domestic construction (as detailed in AS/NZS2859.1—Australian and New Zealand standards) and requires a three coat system, consisting of:                    i. tape (or base) coat            ii. second coat, and            iii. finish (or topping) coat.                        
TABLE 1Summary of “Level of Finish” Dependent Installation RequirementsMax. FrameJoint between Frame MembersJointing and FinishingLevelAlignmentand Back-blockAdhesive +FastenerButt and RecessedofDeviationCeilingsWallsFastenerOnlyJoints Internal andFinishmmButtRecessedButtRecessedFixingORFixingExternal Corners34————✓OR✓{circle around (1)}Tape Coat + SecondCoat44✓{circle around (3)}✓{circle around (2)}—✓OR✓{circle around (1)}Tape Coat + SecondCoat + Finish Coat53✓✓✓{circle around (2)}—✓OR✓{circle around (1)}Tape Coat + SecondCoat + Finish Coat +Skim Coat to the entiresurfaceKey to Symbols: — = Not Applicable. ✓ = Mandatory,{circle around (1)} Not permitted for unseasoned timber.{circle around (2)} Where a butt joint in a wall is less than 400 mm long and is located more than 2 metres from the floor, there may be no need to provide backblocking.{circle around (3)} Back-blocking required where 3 or more recessed joints occur in a continuous ceiling area.It should be noted that, generally, domestic applications should be prepared to a minimum level 4 finish unless specifically a higher or lower level of finish is agreed to by all contracting parties.
Conventional jointing and finishing systems utilise two elements to achieve the necessary compressive and tensile strength in the joint between adjacent plasterboard sheets. These two elements are a paper tape and a compound. Jointing compounds are classified as either setting type or drying type. Setting type compounds reduce installation delays and shrinkage associated with drying-type compounds. They are recommended for experienced trades people and have a defined initial setting time e.g. 45 or 60 minutes. Conventionally, both setting type compounds are beta hemihydrate plaster based.
Plaster is a relatively harmless dry powder made from crushing and heating gypsum rock (calcium sulfate dihydrate) CaSO4 2H2O. The mineral gypsum is commonly found throughout the world, with vast deposits in various countries. It has a wide range of uses, and a particularly important application is its use as a building material.
There are two basic categories of plaster that are in use today, being alpha hemihydrate (alpha gypsum) and beta hemihydrate (beta gypsum). Alpha gypsums calcined under pressure are called gypsum cements. As a result of characteristics such as low water requirement and a more uniform crystal structure, alpha gypsum products are harder and stronger with limited absorptive power and are used primarily when greater strength is required.
Beta hemihydrates are known as industrial plasters, plaster of paris, kettle plaster and kettle stucco. Beta hemihydrates are made by calcining in a kettle at atmospheric pressure. They require more water to make a workable slurry because of their irregular crystalline structure.
Casts made with beta hemihydrates are not as hard as the alpha gypsums. The beta plaster casts are easier to carve and scrape. Low relative cost is the reason why beta hemihydrate is typically used as the basis for the compounds used for conventional plasterboard joints. When combined with additives which modify the rheology, adhesives and water retention qualities, beta plaster-based cements allow the installer to easily trowel the compound onto the joint, thereby providing a suitable “Level 4” or “Grade 4” finish.
Examples of suitable types of setting type compounds are manufactured and sold by CSR Building Products Limited under the trade names “Gyprock® Base Coat 20”, “Gyprock® Base Coat 45”, “Gyprock® Base Coat 60” and “Gyprock® Base Coat 90”. Additional coats may be applied over setting type compounds once they have gone hard (set), usually between 40 to 90 minutes. A drying type compound must be used as a finish coat and must be completely dry before sanding. This usually takes about 24 hours, depending on the weather conditions.
Examples of suitable drying type compounds are manufactured and sold by CSR Building Products Limited under the trade name “Gyprock® Wet Area Base Coat”, “Gyprock® Jointmaster Topping”, “Gyprock® Premixed Total Joint Cement”, “Gyprock® Total Coat-Lite”, “Gyprock® Easy Finish”, “Gyprock® Easy Flow”, and “Gyprock® Pro-Lite Topping”. These products are premixed, and “Gyprock® Total Coat-Lite” is also available in dry powder form. Drying type compounds will shrink and harden when their water content evaporates. Joints must be completely dry before sanding. Actual drying times will be extended in low temperature and high humidity conditions. A setting type compound should not be used over a drying type compound. All compounds can be applied by hand tools or with mechanical jointing tools.
As discussed above, conventional jointing and finishing systems utilise a paper tape and a compound. In order to achieve a joint of a suitable finish grade (typically a minimum of “Level 4” for internal domestic installations), the following steps are followed:
Step 1—Mixing the Compound
The first step to achieving good jointing is correctly mixing the compound. It is important that clean containers and mixing equipment are used, as contamination by previously set compound will accelerate the setting time of the compound. Clean water of drinking quality should also be used to mix the compound. Care should be taken to never mix different compounds together or mix old batches with new ones. This ensures that the compound will set correctly. Incomplete setting compromises the strength of the joint. Short setting time can result in product being wasted.
Additional care must be taken when performing conventional jointing and finishing in extreme weather conditions. For example, when setting type compounds are used during hot, dry conditions, rapid evaporation of water and increased absorption by the lining surface can prevent the compound from setting correctly. This will result in the compound being soft and weak. Also, many drying-type compounds should not be used when the interior temperature is less than 10° C., however CSR compounds can be used at temperature as low as 4° C.
Step 2—Preparation
Any voids deeper than 4 mm and gaps greater than 3 mm wide must be filled with a base coat, which must then be allowed to dry before jointing. All surfaces must be free of dirt, oil or foreign matter that could reduce bond integrity.
Step 3—Application of Paper Tape
Once the recess in the plasterboard sheets have been filled with the compound, a paper tape is bedded over the joint and is lightly covered with the compound. All fastener heads and any surface damage are also filled with the compound and the compound is allowed to set for an appropriate amount of time (typically 60 min for setting type compound and 24 hrs for drying type compound).
Step 4—Second Coat
When the tape coat (which is applied in step 3) is sufficiently dry, a second coat of compound, typically about 170 mm wide, is applied. This second coat is typically finished slightly above the plasterboard surface and utilises feather joint edges. The fastener heads are covered with a second coat of compound, laid in a different direction to the first coat, and extending beyond the first coat, typically by about 25 mm. Again, the second coat of the compound is allowed to set for an appropriate amount of time (typically 60 min for setting type compound and 24 hrs for drying type compound).
Step 5—Finish Coat
When the second coat of the compound is dry, a thin, third finish coat of topping compound is centrally applied over the previous coat (which is applied in step 4). Typically, this topping compound is applied in a layer about 250 mm wide. The outer edges of the newly applied finish coat are sometimes softened by a damp sponge or water brush before the edges are feathered with a trowel. A third layer of the finish coat being the topping compound is applied to the fastener heads, laid in a different direction to the second coat, and extending beyond the second coat by about 25 mm.
Step 6—Sanding
After the finish coat has dried sufficiently (typically at least 24 hrs), the finish layer is sanded smooth with 150 grit paper or cloth or with 220 grit sanding mesh. It is important to avoid excessive pressure, which may scuff the plaster linerboard.
As can be appreciated, the conventional process for jointing and finishing of plasterboard sheets is relatively complicated, time consuming and requires a relatively skilled installer to achieve a joint of sufficient integrity and suitable level of finish achieving a desirable aesthetic appearance.
Therefore, it would be advantageous to provide an improved plasterboard jointing system. This would overcome at least some of the disadvantages of previously known approaches in this field, or would provide a useful alternative.